Human factors engineering, known in Europe as ergonomics, gained initial impetus from sophisticated developments in military technology which presented unfamiliar problems to operators. Solutions required team-work involving specialists in human characteristics – anatomists, physiologists and psychologists – and engineers to make the man-machine combination an effective unit. Success of this inter-disciplinary approach led to its later extension to industrial and non-vocational contexts, inevitably embracing sport and recreation. Many examples are provided in McCormick’s (1976) elaborate textbook.
Ergonomists systematically apply relevant information about human characteristics and behaviour in the design of objects, facilities and environments people use in the various aspects of their lives. (Useful source texts include Murrell, 1965; Kraiss and Moraal, 1976.) The focus is on the individual upon whom the task and environment are seen to impose specific physical, physiological and mental loading. The common strategy is to analyse human responses to these loads so that efficiency, comfort, safety or well-being is increased. Compared with industrial employees, athletes operate mostly close to maximal levels since competition is inherent in sport which usually involves heavy work: both, however, desire a working environment conducive to safe and efficient performance.
As the scope of ergonomics is extensive (in terms of its body of knowledge, problems tackled and methodologies available), detailed treatment is impractical here. The following sections attempt to highlight the more dominant general approaches and themes in human factors engineering.
A recurrent theme in ergonomics is the concept of limited human capacity. This applies to such aspects as aerobic power and physical working capacity, anaerobic power, strength, reactions, stress tolerance, information processing and so on. The implication is that a ceiling is placed on current functional ability. The individual will be unsuccessful, perhaps suffering injury, if task demands outstrip the capacity to meet them. Grandjean’s (1969) text entitled ‘fitting the task to the man’ is representative of the classical approach.
In games, demands may be distributed unevenly as shown by the work rate of top soccer players expressed as distance covered per match . The underlying pattern is that endurance is demanded most of midfielders while anaerobic power is emphasised in centre-backs. Without the specific requirements for these positions the individual is forced to play at an inferior level, to attempt to alter his capacity by appropriate training or to switch to a position more compatible with his current capabilities. Tailoring task demands to the individual has been a special hallmark of classical ergonomics. If in sport the individual and his task are poorly matched the outcome may be gross under-achievement or alternatively breakdown through injury.
The classical approach suggests implications for training and selection of athletes and for injury prevention. Analysis of competition demands, provides the framework on which training regimes can be devised and helps locate where competitors are particularly liable to incur injury. Fitness testing helps evaluate preparedness for competition on a scientific basis and can assist in team selection as well as indicate specific individual weaknesses which appropriate training can then remedy. This is the broad rationale behind the testing of elite athletes in ‘centres of excellence’ in various countries. Monitoring fitness status throughout pre-season and competitive periods is advocated, as specific fitness parameters fluctuate. Time of day of performance is also relevant since many human functions show a circadian variation. As fitness has many facets, an inter-disciplinary approach is usually most effective. Psychological, anthropometric and physiological tests should be incorporated into a multivariate battery to provide a comprehensive profile since there are personality and temperament as well as biological and physical determinants of athletic success .
Fitness testing helps also to determine the effectiveness of training programmes. The quest for an optimum regime based on sound scientific principles has attracted numerous researchers. Beneficiaries would include the habitually sedentary undertaking physical training for positive health and athletes undertaking severe conditioning schedules. The aim of training is to fit the individual to the task and allow realisation of potential. The degree to which even an optimal training stimulus can increase current capacity is itself limited and varies with the individual, the initial fitness level and the biological system being conditioned. As differences among individuals are generally greater than the maximal training effect, genetic factors are obviously important for a good performance potential. Greater attention to selection than training may be more attractive to coaches where the task is relatively inflexible. For team games a compromise is usual, preparation consisting of harmoniously fitting each individual for his job and fitting the job to the individual by appropriate training, selection and team tactics.
STRESS AND STRAIN
The concept of stress
Objectives of human factors engineering include the maintenance or enhancement of certain human values such as health, safety, satisfaction and well-being. Essentially this amounts to avoiding the adverse effects of stress which is often blamed as the main source of many malaises. Stress is a difficult concept to pin down since the meaning assigned to it varies with the individual discussing or investigating it. It has been the subject of study in medicine, psychiatry and sociology as well as in the scientific disciplines contributing to sports ergonomics. Ramifications of the concept and its relationship to mental and physical loadings are treated in detail by Singleton et al (1971).
Disillusion may be expressed with the concept of stress often presented. Some clarification is obtained by adopting the engineering convention of using stress in the sense of a deforming force or stressor, and strain for the resultant deformation. The reaction can be monitored using psychological, physiological or biomechanical techniques. This viewpoint has proved consistently rewarding in analyses of occupational stress by highlighting sources of emotional strain, peak physiological loading and imperfect working postures. These avenues can equally be explored in sporting contexts where most suitable techniques tend often to be non-invasive. Assessment of physiological strain may involve measurement of the oxygen consumption level, heart rate, body temperature, or electromyo-gram, for example. Physical strain is often only manifested when injury is apparent:, analysis of injury records may be sometimes a useful starting point for investigation. Psychological strain too may be camouflaged and difficult to uncover. It may be either transient pre-competition or a more persistent emotional burden.
Imminent competition usually brings transient emotional strain. The nervous system prepares the individual for the forthcoming contest with elevated anticipatory responses.
Emotional tachycardia has been used to indicate the pre-event stress in various sports. It is conceivable that the thrill of courting danger provides part of the attraction to participants and spectators in these sports. Individuals can habituate to stress while top athletes manage to harness it successfully for their benefit.
A certain amount of stress is desirable for the athlete to be optimally aroused to perform while performance deteriorates with over-arousal. Psychological states indicating emotional vigour have been shown to correlate with performance in cross-country running (Reilly, 1977). The finding of a relationship between injuries and anxiety in soccer (Thomas and Reilly, 1975) suggested psychological reactions beyond an optimal level. Though such results are understandable in hindsight, prediction of performance or injury from stress indices is fraught with difficulty .
Psychological strain may manifest itself during competition in errors in performance. These signal the start of a train of events which may lead to an accident and possible ensuing injury. Unforced errors and critical incidents where accidents nearly happen merit close attention in sports accident analyses which tend to be investigated retrospectively. Study of errors also provides valuable information for the coach. Eliminating precursors of errors, whether they are related to psychological or fitness factors or extraneous to the individual in origin, is immensely useful in reducing the incidence of injury. Intracompetition stress may also be reflected in increased aggressiveness and readiness to engage in conflicts. Since dangerous play could be promoted as a consequence, remedial coaching may be necessary.
Emotional strain may also exert itself in insidious adverse changes in morale. This will be especially relevant where competition is over an extended period with chronic emotional strain a possible outcome. Long-term subjection to intense competition may bring its own specific psychological wear and tear, a lot depending on the extent to which enjoyment and success can be preserved. Unfavourable changes include deterioration in vegetative functioning with poor appetite and sleep, and ultimately impairment in coordination and fine motor skills. A drawback of success in prolonged knock-out competitions is the more cluttered fixture list with reduced recovery between matches that results. Playing four soccer matches within ten days was reported to cause hyperfunction and enlargement of the thyroid which could lead to aggressive behaviour under the tension of competition (Andrejevic, 1973). Elevated levels of stress hormones in the urine of players were also found. In this sport goalkeepers show the greatest susceptibility to stress-induced ulcers because of the responsibilities of this role, while the highest incidences among players and coaches coincide with the season’s peak period. Psychosomatic effects are described in detail in the general adaptation syndrome of Selye (1956). Dietary, pharmacological and physiotherapeutic methods have been suggested as remedies as well as varied regimes of training and relaxation. It should be conceded, however, that some players thrive on frequent competition so that it is imperative for the coach or trainer to know each individual well.
Group factors are evident in that stability of team composition is an important element in the development of sustained success in games. Individuals get to know each other’s play intimately, team spirit is rein- forced and tactical efficiency improves with familiarity. Frequent changes in personnel clearly militate against group morale and competence. A consistent line-up assumes absence of injuries so their avoidance is an important contribution towards victories achieved. Psychological counselling is often used at international playing level to maintain group cohesion, as poor individual morale can easily affect the whole team. Though harmony between members is undoubtedly associated with team success, it is not easily established whether it is the result or the determinant of that success.
THE SYSTEMS APPROACH
Many human factors problems, especially when associated with technology, are tackled by systems analysis. A system is defined as an assemblage of functional units with a common overall purpose and forming a connected whole. It can apply equally to a sports medical unit, a football team, a water-skier in tow or a biological system. The systems approach implies knowledge of the objectives, the input and output, while various aspects of system behaviour may be considered. (For further discussion the reader is referred to Singleton, 1974.) Discrepancies between input and output are especially relevant to accident analysis.
The ergonomist is particularly concerned with how the human harmonises with the other system elements. In operational systems, control is implemented by means of various control devices such as the pedals and handlebars of a bicycle or the joystick and steering wheel of a power boat. Frequently, computer assistance is enlisted as in regulating ski-resort usage for avoiding congestion and reducing accidents on the slopes. Whatever the system the fundamental human functions relate to information input, information processing, decision making and action or response. In serial tasks involving continuous control there is always some form of feedback to the operator: this allows frequent error correction and helps prevent accidents occurring.
Man-powered flight provides an example of problems related to control devices in a man-machine system. Conventional designers concentrated on the operator as an aero-engine and ignored the mental loading induced by having to guide the aircraft while simultaneously producing high power output. Since the crafts have large wing spans and operate best close to ground, the margin for error is considerably less than for gliding or normal flying. The type of movement optimising control of pitch, roll and yaw can be determined on a rig comprising an electronically controlled tracking task fitted onto a bicycle ergometer (Evans and Reilly, 1979). Since field studies are impractical because of the high frequency of crashes the simulator described is useful for training potential man-powered craft pilots.
Simulation consists of reproducing or representing an actual or conceptual object, system, process or theoretical construct. It is used in ergonomics research where carrying out the investigation in real life circumstances is impractical or dangerous. It provides an opportunity to test the reactivity of a number of variables in advance without committing resources or operators to risk. Mechanical models may be used in accident simulation to investigate impact stresses in various sports and evaluate equipment designed to protect against injury. Variations in environmental temperature, humidity and pressure can be simulated in an environmental chamber and investigated without recourse to the cost and inconvenience of travelling to their locations. The dynamics of the cardiovascular responses can be studied by computer simply by altering electrical voltages.
The systems approach has stimulated much detailed study of human movement. Insight into the processes of skills acquisition, motor learning and proprioception has followed from inspired applications of control theory. Uses in sport of biofeedback, the presentation of biological signals to the individual generating them, have systematically unfolded. These include applications in reducing anxiety, neuromuscular training in rehabilitation and assisting skill acquisition.
Engineering the environment
Much attention in industrial ergonomics has been given to environmental factors. It is important to consider also the physical environment in which training or competition takes place. This is often the source of various stressors whether thermal, barometric, noise or pollution. Though much is known about the effects of discrete environmental stressors there is still a lot to be learned on how they interact when in combination. In outdoor sports the environment to be experienced can sometimes be foreseen and protected against. In man-built arenas it can be engineered so that human efficiency and comfort are promoted.
The essence of the schematic work station analysis is that the design process starts by concentrating on the human and works outwards. The task and interface are then considered in turn. The workspace is constructed around these before factors in the physical environment complete the projection. Ergonomics is here an assistant technology to architecture and engineering and can save the embarrassment of forced re-design from mistakes appearing after construction.
Problems associated with heat injury and heat disorders have generated much research attention and medical concern. Heat injury is discussed separately elsewhere . Many equations have been derived as heat stress indices to express the total thermal load. Typically these include composites of environmental measures such as the WBGT Index (incorporating wet, dry bulb and globe temperatures), or predicted physiological responses from combinations of such measures as in the Predicted 4h Sweat Rate (P4SR) devised by McArdle et al (1947). In strenuous exercise, heat loss is mainly by evaporation of sweat from the skin and this avenue of loss is impaired in humid conditions, while cooling is assisted with increased air velocity. Most heat stress indices are, however, not entirely satisfactory for application to sports.
Athletes must often take preparatory rather than avoidance measures since the timing and location of competition are outside their control. Training in the heat allows circulatory and sweating mechanisms to respond by adapting within limits to heat stress. The stress is alleviated by sensible organisation if competitive events likely to produce heat injury are timetabled for the cooler part of the day.
In the case of indoor sports facilities, the environ- ment can be engineered with human comfort as a major criterion. Thermal comfort is determined by air temperature, mean radiant temperature, relative air velocity, humidity, activity level, thermal resistance of clothing, all of which must be considered in deriving a thermal comfort equation (Fanger, 1973). This will help designers of indoor recreation centres, particularly in installing their heating and ventilation systems. Comfort needs of spectators and competitors may conflict as for example in competitive swimming arenas. Environmental engineering can provide acceptable compromises when the total areas and complete workspace are taken into account.
The wind-chill index (Siple and Passel, 1945) has long been used for assessment of extreme cold weather experienced by mountaineers, skiers and sailors. Wet-cold conditions must be safeguarded against by using suitably insulated and waterproof clothing. Garments can easily incorporate synthetic layers and buoyancy provision where water immersion is possible. After accidental immersion, heat loss is accelerated by the convective currents created in swimming so that imminent rescue is best awaited. Effective protective clothing for all cold conditions must secure the microclimate to which the skin is immediately exposed.
Neuromuscular function deteriorates with lowered temperatures so that accidents are promoted by declining motor performance. The hands cool especially rapidly and some strength as well as dexterity is lost. Frostbite is caused by ice crystals forming in the tissues and occurs first on the fingers, toes, nose and ears. Ulcers result in the affected areas which are slow to heal. Chilblains, which are chronic inflammatory swellings, can develop in the extremities from repeated exposures to cold insufficient to cause frostbite. Shivering represents an autonomic attempt to generate heat by involuntary muscle activity and wards off hypothermia. When the body’s core temperature reaches about 32 °C (89.6 °F), shivering is replaced by permanent muscular rigidity and consciousness is gradually lost. This temperature is usually taken as the critical level of hypothermia though it is subject to controversy.
There is still much wanting in the design of clothing for a variety of outdoor winter sports that will afford protection against the weather and provide the mobility needed for unhampered activity. Products can be validated using physiological criteria in rain-sheds or environmental chambers and in the field, while mobility and durability are further requirements.
Hypoxia or lack of oxygen is associated with sport performance at altitude. Discomfort on exposure can lead to ‘mountain sickness’ with symptoms including nausea, dizziness, headaches and sleeplessness. The main cause is hyperventilation which washes co2 out of the blood, disturbing its acid-base balance. Effects of visiting high altitudes have been observed in balloon-ists and parachutists, and in climbers attempting to scale the Himalayan peaks. Highly trained individuals tend to suffer less and acclimatise more quickly than those who are untrained. Strenuous activity can cause respiratory distress at moderate altitudes in sedentary individuals, a risk often ignored by unfit American adults flying to the Colorado mountains for skiing without prior conditioning.
With increasing altitude, atmospheric pressure falls causing a reduction in alveolar oxygen tension and in the oxygen saturation of the blood. Endurance performance deteriorates in consequence. Arterial oxygen saturation does not decrease at the same rate as alveolar partial pressure but does decline fairly rapidly after 3 000m. Olympic performances at 2 240m in Mexico 1968 were evidence of the adverse effects on endurance. The value of acclimatisation was demonstrated in that all gold medallists in running events at 1 500m and upwards were trained or living at altitude. In sprint events, which are not dependent on oxygen supply to the tissues, performances are actually assisted by the reduced air density.
Normally at 8 000 to 9 000m oxygen saturation falls to a point where the brain is inadequately provided with oxygen and unconsciousness usually follows. Humans can, however, acclimatise to these altitudes when sufficient and proper training procedures are used. The successful Everest ascent (8848m) in 1978 unsupported by oxygen equipment is evidence of this. Mount Nuptse (7 833m) in the Himalayas was climbed without fixed camps or oxygen by a British group a year later.
Training resorts have been established in various countries with high plateaux so that athletes can acquire the physiological benefits associated with respiratory and circulatory adaptation to altitude for improving sea-level performances. As responses are individualistic their use may be unsuitable for many athletes, and sea-level results can be adversely affected by previous exposure to altitude. Some may be more vulnerable than others to effects of moderate and high altitude and require longer periods of adjustment. For those who might benefit the altitude, duration and frequency of exposure, and the timing of the return to sea-level before competing are critical. Where competition is at altitude, natives are endowed with a physiological heads tart.
Conversely pressure increases the greater the depth underwater. Risks to which divers are exposed in this hyperbaric environment are discussed in 0. Though the underwater habitat is alien to man, Scuba and wet-suits make prolonged submersion possible. The pleasurable feelings associated with nitrogen narcosis known as ‘raptures of the deep’ illustrate that pleasant sensations are not necessarily conductive to optimal performance. At a simulated dive of 46m increased feelings of well-being have been found to accompany deteriorating performances (Thomas and Reilly, 1974). Because of these mental states divers tend to over-estimate their information processing capacity and commit errors of judgement.
Noise and lighting
The ears and eyes are delicate sensory mechanisms so the level of noise and lighting are important environmental aspects. Attention to acoustical features can appreciably benefit the comfort of indoor arenas. Surprisingly high noise levels are sometimes found in poorly designed pools when heavily crowded with young swimmers. Motor-racing and motor-cycling constitute hearing hazards for spectators close to the embankments. Ear protectors are essential for mechanics working in proximity to these sports vehicles for long periods. Shooters are subjected to high values of impulsive sound and significant noise doses in the range of 130 to 160 dB. Other potential sources of noise hazard include snowmobiling and careless use of starting pistols. Athletes subject to noise stress at work or to frequently standing close to amplified disco music are also vulnerable.
Middle ear deafness is usually caused by a stiffening and damping of the ossicles through which sound waves are transmitted to the inner ear. Alternatively there may be an infection in the middle ear, obstruction of the Eustachian tube or perforation of the ear drum causing hearing loss. Medical treatment or amplification by means of a hearing aid can be successful as long as the inner ear is intact. If the special receptor cells in the inner ear or the nerve trunks leading to the hearing centre in the brain are damaged amplification is ineffective. Nerve deafness may be due to severe head injuries, infections or exposure to high noise levels. The only way of avoiding risk of ear damage is by wearing protective devices, the fluid seal type of ear muff offering the best security.
Indoor sports facilities require artificial illumination which must meet the various sports association’s standards: in ball games the faster the activity the more vital is the need for good lighting. Glare often disturbs performers, usually emanating from polished floors or adjacent glass panelling. Contrasting background may be important against which to judge the flight of, say, a badminton shuttle or squash ball. Attention to these features is often neglected in the design of sports facilities, including floodlit outdoor areas.
THE IMMEDIATE INTERFACE
Equipment design can prevent injuries in three main ways. Firstly, quality control in production ensures injury is not encouraged by provision of faulty equipment. Secondly, strain is avoided if equipment matches individual needs and characteristics: the designer is referred initially to manuals such as Woodson and Conover (1966). Compatibility may necessitate a range of fabrications within the limits of current governing body standards. Controls, displays and workspace may be embraced as in the design of powered sea or terrestrial vehicles. The physical properties of the equipment, ease of operation, anthropometry and subjective responses of users are consistently relevant. Thirdly, effective and comfortable protective equipment can be provided to cushion individuals against harmful impact or environmental influences.
Sports equipment covers all aspects of interfacing the performer with the environment and includes clothing, footwear, implements, rackets and sports machines. Historically, man contrived equipment to extend his power and mobility: evolution of implemen-tal, racket and machine sports is the direct result of this enhanced capability. Technological innovations, such as use of fibre-glass materials in sports, aid perform- ance but in some cases require modification of existing competition rules before improvement can be realised. Often games skills need altering for a smooth changeover.
Footwear has tended to be more a matter of fashion and market forces, and so is often implicated in sports injuries. Ideally, shoes should be designed for specific sports and surface qualities. Biomechanical analysis and development of techniques such as pedobarogra-phy provide methodologies for validating current and new products which the customer could only benefit from. Swimfins assist movement underwater but their surface area and flexibility determine to what extent. The type of ski-binding, particularly the mode of release in falling, affects the type and frequency of injury (Shealy et al, 1974). The current international standard for setting ski-bindings has been shown by Pope et al (1976) to be invalid.
Special effort has been devoted to protecting the head in sport. This appears related to three factors -skull deformation, intracranial pressure and rotational motion. (Dynamic impact tests are preferable in determining the stiffness of materials for use as helmet liners.) Helmets are worn in a variety of activities from skateboarding to tobogganing. Effective headgear reduces the acceleration of the head when it is hit as well as attenuates compression forces. Mouthguards constructed over an accurate model of the wearers’ teeth similarly lower the intracranial pressure from a blow on the chin. Special helmets with ear holes have been developed for hang-gliding so the pilot can sense air flow for a more accurate adjustment of his speed. In games the helmet may be used illegally as a weapon to butt opponents. In many sports the problem of protection is of such a magnitude that a helmet alone cannot supply total protection and additional modifications to the playing environment must be undertaken.
Interface also involves characteristics of the playing surface. Determination of the best flooring material for the various activities conducted in multi-purpose facilities is an area where the materials scientist, architect and human scientist can usefully cooperate. In multi-purpose sports halls the floor should be reasonably resilient, non-slip, non-reflective, should give a true bounce and roll, have good background colour, easy maintenance, be resistant to all types of footwear used and be non-abrasive. Special flooring considerations obtain for certain activities; squash courts should be capable of absorbing sweat falling from players while floors in weight-training areas must withstand possible damage from heavy pieces of equipment.
Synthetic turf for outdoor games must be waterproof, resistant to ultra-violet degradation and permit ball and play behaviour similar to natural turf. The development of synthetic indoor and outdoor surfaces has been due to their economic and organisational advantages. Artificial surfaces are often blamed for injuries and are rarely laid with human characteristics foremost in mind. The indoor running track at Harvard, with a surface polyurethane cover on a substrate consisting primarily of wood, provides an exception. The compliance of the track was set specifically to match the stiffness of human muscle determined after detailed experiments. Improved performances and reduced injury rates were reported to result (McMahon and Greene, 1978).
The majority of tests currently employed for artificial turf and synthetic surfaces are related to materials science more than human factors criteria. Those used invariably include durability, spike penetrability, crumb retention, inflammability, abrasive wear criteria, for example. Resistance, stiffness and friction tests should be added as a matter of course for more effective shoe/surface interface. For outdoor games surfaces, soil penetrability tests would provide a more objective means for choice of footwear and studs than the arbitrary heel plant into the ground usually employed pre-match.
Mismatch between the sportsman, his task and the performance environment can leave the individual at risk. An understanding of the effects of stressors can help to prepare the individual to meet them or eliminate environmental influences that are possibly damaging. In many cases an intuitive adaptation occurs in top performers, skills and work rate being altered to suit the conditions.
The craving continually to improve existing records leads to a search for better equipment as well as training methods. Frequently, safety is sacrificed for efficiency, a concession unacceptable to those concerned with sports accidents and injuries. Attention to ergonomic or human factors aspects at the design stage can encourage acceptable compromises.
Andrejevic, M. (1973). Sports medicine in football. In Proceedings of international symposium on the medical aspects of soccer (football). CONCACAF, Toronto.
Astrand, P. O. (1967). Physical activity and cardiovascular health: commentary. Canadian Medical Association Journal, 96, 760.
Evans, A. D. B. and Reilly, T. (1979). Design of a simulator for investigation of control functions in man-powered flight. Paper presented at the Society of Sports Sciences Conference (Leeds).
Fanger, P. O. (1973). Thermal comfort. McGraw-Hill, New York.
Goodwin, A. B. and Cumming, G. R. (1966). Radio telemetry of the electrocardiogram, fitness tests and oxygen uptake of water polo players. Canadian Medical Association Journal, 95, 402-406.
Grand jean, E. (1969). Fitting the task to the man. Taylor-Francis, London.
Johnson, W. R. (1949). A study of emotion revealed in two types of athletic sports contest. Research Quarterly, 20, 72-79.
Kraiss, K. F. and Moraal, J. (1976). An introduction to human engineering. Verlag TUV Rheinland Gmbh, Koln.
McArdle, B., Dunham, W., Hollong, H. E., Ladell, W. S. S., Scott, J. W., Thomson, M. L. and Weiner, J. S. (1947). The prediction of the physiological effects of warm and hot environments. Medical Research Council Report No. RNP 47/391, London.
McCormick, E. J. (1976). Human factors engineering and design. McGraw-Hill, New York.
McMahon, T. A. and Greene, P. R. (1978). Fast running tracks. Scientific American, 239, 112-121.
Murrell, K. F. H. (1965). Ergonomics. Chapman and Hall, London.
Pope, M. H., Johnson, R. H. and Etdinger, C. F. (1976). Ski binding settings based on anthropometric and biomechanical data. Human Factors, 18, 27-32.
Reilly, T. (1975). An ergonomic evaluation of occupational stress in professional football. Unpublished PhD Thesis, Liverpool Polytechnic.
Reilly, T. (1977). Pre-start moods of cross-country runners and their relationships to performance. International Journal of Sports Psychology, 8, 210-217.
Reilly, T. and Thomas, V. (1976). A motion analysis of work-rate in different positional roles in professional football match-play. Journal of Human Movement Studies, 2, 87-97.
Schneider, E., Angst, F. and Brandt, J. D. (1978). Biomechanics in rowing. In E. Asmussen and K. Jorgensen (eds). Biomechanics VI-B. University Park Press, Baltimore.
Selye, H. (1956). The stress of life. McGraw-Hill, New York.
Shealy, J. E., Geyer, L. H. and Hayden, R. (1974). Epidemiology of ski injuries: effects of skill acquisition and release-binding on accident rates. Human Factors, 16, 459-473.
Singleton, W. T. (1974). Man-machine systems. Penguin books, Harmondsworth.
Singleton, W. T., Fox, J. J. and Whitfield, D. (1971). Measurement of man at work. Taylor-Francis, London.
Siple, P. A. and Passel, C. F. (1945). Measurement of dry atmospheric cooling in subfreezing temperatures. Proceedings of American Physiology Society, 89, 177-199.
Skubic, V. and Hilgendorf, J. (1964). Anticipatory exercise and recovery heart rate of girls as affected by four running events. Journal of Applied Physiology, 19, 853-856.
Taggart, P. and Gibbons, D. (1967). Motor car driving and the heart rate. British Medical Journal, I, 411-412.
Thomas, V. and Reilly, T. (1974). Effects of compression on human performance and affective states. British Journal of Sports Medicine, 8, 188-190.
Thomas, V. and Reilly, T. (1975). The relationship between anxiety variables and injuries in top-class soccer. Proceedings European Sports Psychology Conference (Edinburgh).
Vanek, M. and Cratty, B. J. (1970). The psychology of the superior athlete. Macmillan, London.
Woodson, W. E. and Conover, D. W. (1966). Human engineering guide for equipment design. University of California Press, Los Angeles.